Structure and method to expose memory cells with different sizes

ABSTRACT

A method of forming a memory device is provided. In some embodiments, a memory cell is formed over a substrate, and a sidewall spacer layer is formed along the memory cell. A lower etch stop layer is formed on the sidewall spacer layer, and an upper dielectric layer is formed on the lower etch stop layer. A first etching process is performed to etch back the upper dielectric layer using the lower etch stop layer as an etch endpoint.

REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of U.S. application Ser. No. 16/916,415, filed on Jun. 30, 2020, which is a Continuation of U.S. application Ser. No. 16/220,200, filed on Dec. 14, 2018 (now U.S. Pat. No. 10,727,077, issued on Jul. 28, 2020), which is a Divisional of U.S. application Ser. No. 15/883,748, filed on Jan. 30, 2018 (now U.S. Pat. No. 10,163,651, issued on Dec. 25, 2018), which claims the benefit of U.S. Provisional Application No. 62/564,360, filed on Sep. 28, 2017. The contents of the above-referenced Patent Applications are hereby incorporated by reference in their entirety.

BACKGROUND

Many modern day electronic devices contain non-volatile memory, which is able to store data in the absence of power. Non-volatile memory such as magnetoresistive random-access memory (MRAM) and resistive random access memory (RRAM) are promising candidates for next generation non-volatile memory technology due to relative simple structures and their compatibility with complementary metal-oxide-semiconductor (CMOS) logic fabrication processes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1A illustrates a cross-sectional view of some embodiments of a memory device with an etch stop layer.

FIG. 1B illustrates a cross-sectional view of some alternative embodiments of a memory device with an etch stop layer.

FIG. 2 illustrates a cross-sectional view of some embodiments of an integrated circuit with the memory device of FIG. 1A or FIG. 1B.

FIGS. 3-7 illustrate a series of cross-sectional views of some embodiments of a memory device at various stages of manufacture.

FIG. 8 illustrates a flow diagram of some embodiments of a method for manufacturing a memory device.

FIGS. 9-13 illustrate a series of cross-sectional views of some alternative embodiments of a memory device at various stages of manufacture.

FIG. 14 illustrates a flow diagram of some alternative embodiments of a method for manufacturing a memory device.

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples, for implementing different features of this disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “top,” “bottom,” “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Moreover, “first”, “second”, “third”, etc. may be used herein for ease of description to distinguish between different elements of a figure or a series of figures. “First”, “second”, “third”, etc. are not intended to be descriptive of the corresponding element. Therefore, “a first dielectric layer” described in connection with a first figure may not necessarily correspond to a “first dielectric layer” described in connection with another figure.

A non-volatile memory device includes a memory cell array having a plurality of memory cells. Each of the memory cells includes a top electrode and a bottom electrode separated by a switching dielectric. Depending on a voltage applied to the pair of electrodes, the switching dielectric will undergo a reversible change between a high resistance state associated with a first data state (e.g., a ‘0’ or ‘RESET’) and a low resistance state associated with a second data state (e.g., a ‘1’ or ‘SET’). The memory cell is compatible with complementary metal-oxide-semiconductor (CMOS) logic fabrication processes and can be inserted between a lower metallization line and an upper metallization line for data storage and transmission. In some applications, the memory device may include memory cells with different sizes. The memory cells may have different lateral dimensions as well as different vertical thicknesses. Thus a height from the lower metallization line to a top electrode of a memory cell can vary depending on the memory cell size. The variation of the vertical heights makes it a challenge to expose the top electrodes of memory cells with different sizes during the fabrication: a top electrode of a smaller memory cell may not be well exposed until another top electrode of a larger memory cell is damaged.

The present application is related to an improved memory device having an etch stop layer lining a memory cell, and corresponding manufacturing methods. In some embodiments, referring to FIG. 1A or FIG. 1B for example, a memory device comprises a first memory cell 114 a and a second memory cell 114 b disposed over a substrate 102. Each of the memory cells 114 a, 114 b comprises a bottom electrode 112, a switching dielectric 116 disposed over the bottom electrode 112 and having a variable resistance, and a top electrode 118 disposed over the switching dielectric 116. The bottom electrode 112 is coupled to a bottom electrode via 110 surrounded by a lower dielectric layer 108. A sidewall spacer layer 126 is disposed over the bottom electrode via 110 and the lower dielectric layer 108 and extends upwardly along sidewalls of the bottom electrode 112, the switching dielectric 116, and the top electrode 118. A lower etch stop layer 120 is disposed over the lower dielectric layer 108 and lining an outer sidewall of the sidewall spacer layer 126. An upper dielectric layer 136 is disposed on the lower etch stop layer 120 and surrounding an upper portion of the sidewall spacer layer 126. The lower etch stop layer 120 is made of a dielectric material that can protect the memory cell 114 a, 114 b during polishing and etching processes for top electrode exposure. For example, the lower etch stop layer 120 and the upper dielectric layer 136 may be formed overlying the memory cell 114 a, 114 b (see FIG. 4 for example) and then subject to an etching back process to expose the top electrode 118 (see FIG. 6 for example). The lower etch stop layer 120 may comprise a dielectric material having a distinct etch selectivity from the upper dielectric layer 136 with respect to the etchant of the etching back process, such that the lower etch stop layer 120 can be retained and protect the top electrode from damage. Thereby, the polishing and etching processes can be better controlled and the top electrode 118 of the memory cell 114 a, 114 b can be well exposed after a more precise controlled removal of the lower etch stop layer 120.

The bottom electrode 112 of the memory cell 114 a, 114 b is a conductive material, such as titanium nitride. The bottom electrode 112 may also comprise, for example, titanium, tantalum, tantalum nitride, platinum, iridium, tungsten, ruthenium, or the like. In some embodiments, the memory cell 114 a, 114 b is a magnetoresistive random access memory (MRAM) cell and the switching dielectric 116 can comprise a magnetic tunnel junction (MTJ) structure having a bottom ferromagnetic layer and a top ferromagnetic layer separated by a tunnel barrier layer. In some other embodiments, the memory cell 114 a, 114 b is a resistive random access memory (RRAM) cell and the switching dielectric 116 can comprise a RRAM dielectric layer. The switching dielectric 116 may be a high-k layer (i.e., a layer with a dielectric constant k greater than 3.9), for example, tantalum oxide, tantalum hafnium oxide, tantalum aluminum oxide, or another material that includes tantalum, oxygen, and one or more other elements. The bottom electrode via 110 is made of a conductive material, such as platinum, iridium, ruthenium or tungsten. The lower dielectric layer 108 surrounds the bottom electrode via 110 and comprises one or more layers of dielectrics. The lower dielectric layer 108 may comprise silicon carbide, silicon nitride, silicon oxide, or one or more layers of composite dielectric films. For example, the lower dielectric layer 108 may comprise a silicon-rich oxide layer 108 b arranged on a silicon carbide layer 108 a. Through the bottom electrode via 110, the memory cell 114 a, 114 b shown in FIG. 1A or FIG. 1B may be coupled to a bottom metallization line 106 disposed within a bottom interlayer dielectric layer 104. The bottom electrode via 110 may also function as a diffusion barrier layer to prevent the bottom metallization lines 106 material from diffusing into the bottom electrode 112. The bottom metallization line 106 may be, for example, a metal, such as copper. The bottom interlayer dielectric layer 104 may be, for example, an oxide, a low-k dielectric (i.e., a dielectric with a dielectric constant k less than silicon dioxide) or an extreme low-k dielectric (a dielectric with a dielectric constant k less than about 2).

In some embodiments, the top electrode 118 may comprise one or more metal or metal composition layers comprising, for example, titanium, titanium nitride, tantalum, tantalum nitride, or the like. In some embodiments, the top electrode 118 is electrically coupled to the top metallization line 134 through a top electrode via 132 arranged between the top electrode 118 and the top metallization line 134. The top electrode via 132 may be, for example, a conductive material, such as such as copper, aluminum, or tungsten. During operation of the memory cell 114 a, 114 b, voltages are applied between the top electrode 118 and the bottom electrode 112 to read, set, or erase the memory cell 114 a, 114 b by forming or breaking one or more conductive filaments of the switching dielectric 116. Thus the memory cell 114 a, 114 b can have a variable resistance in a comparatively low or high resistance state to stand for low or high bit status, for example.

As shown in a cross-sectional view 100 a of FIG. 1A, in some embodiments, the sidewall spacer layer 126 is disposed directly on the lower dielectric layer 108 and contacting sidewalls of the bottom electrode 112, the switching dielectric 116, and the top electrode 118. The sidewall spacer layer 126 protects the bottom electrode 112, the switching dielectric 116, and the top electrode 118 from shortage. In some embodiments, the top surface of the sidewall spacer layer 126 is lower than that of the top electrode 118, such that an uppermost point of the sidewall spacer layer 126 is located on the sidewall surface of the top electrode 118. The lower etch stop layer 120 is arranged aside of the sidewall spacer layer 126 and directly on the lower dielectric layer 108. In some embodiments, the lower etch stop layer 120 extends laterally between the memory cells 114 a, 114 b, and extends upwardly to cover sidewall and top surfaces of the sidewall spacer layer 126. The upper dielectric layer 136 may be arranged directly on the lower etch stop layer 120. In some embodiments, the sidewall spacer layer 126 is separated from the upper dielectric layer 136 by the lower etch stop layer 120. The upper dielectric layer 136 may have a bottom surface separated from a top surface of the lower dielectric layer 108 by the lower etch stop layer 120. The lower etch stop layer 120 and the top electrode 118 may have top surfaces aligned or coplanar, and may be further coplanar with a top surface of the upper dielectric layer 136. The top electrode 118 may be coupled to a top metallization line 134 through a top electrode via 132. The top metallization line 134 and the top electrode via 132 are surrounded by a top interlayer dielectric layer 138. In some embodiments, bottom surfaces of the top metallization line 134 and the top interlayer dielectric layer 138 and top surfaces of the top electrode 118 and the lower etch stop layer 120 are coplanar. The lower etch stop layer 120 is made of a dielectric material different from that of the sidewall spacer layer 126. The sidewall spacer layer 126 may comprise, for example, silicon nitride. The upper dielectric layer 136 may comprise, for example, silicon dioxide. The lower etch stop layer 120 may be made of silicon oxynitride. During the fabrication process, the lower etch stop layer 120 is more resistive to the etchant (comparing to the upper dielectric layer 136 or the sidewall spacer layer 126) when exposing the top electrode 118, thereby providing extra support and protection to the top electrode 118 from being damaged. For example, the lower etch stop layer 120 may have an etching rate to the etchant about 10 times smaller than the upper dielectric layer 136 or the sidewall spacer layer 126.

As shown in a cross-sectional view 100 b of FIG. 1B, in some alternative embodiments, the sidewall spacer layer 126 is disposed directly on the lower dielectric layer 108 and extends in a lateral direction continuously between the memory cells 114 a, 114 b, while the sidewall spacer layer 126 comprises discrete portions respectively surrounding the memory cells 114 a, 114 b in the embodiments shown in FIG. 1A. The lower etch stop layer 120 is arranged directly on the sidewall spacer layer 126. Thus, the sidewall spacer layer 126 may separate the lower etch stop layer 120 from the lower dielectric layer 108. The sidewall spacer layer 126 extends upwardly and contacting sidewalls of the bottom electrode 112, the switching dielectric 116, and the top electrode 118. In some embodiments, the top surface of the sidewall spacer layer 126 is coplanar with top surfaces of the top electrode 118 and the lower etch stop layer 120. The upper dielectric layer 136 may be arranged directly on the lower etch stop layer 120, and may have a top surface coplanar with that of the lower etch stop layer 120. Similar to the embodiments shown in FIG. 1A, the sidewall spacer layer 126 protects the bottom electrode 112, the switching dielectric 116, and the top electrode 118 from shortage. The top electrode 118 may be coupled to a top metallization line 134 through a top electrode via 132, which are surrounded by a top interlayer dielectric layer 138. In some embodiments, bottom surfaces of the top metallization line 134 and the top interlayer dielectric layer 138 and top surfaces of the top electrode 118, the sidewall spacer layer 126, and the lower etch stop layer 120 are coplanar. The lower etch stop layer 120 is made of a dielectric material different from that of the sidewall spacer layer 126. The sidewall spacer layer 126 may comprise, for example, silicon nitride. The upper dielectric layer 136 may comprise, for example, silicon dioxide. The lower etch stop layer 120 may be made of silicon oxynitride. During the fabrication process, the lower etch stop layer 120 is more resistive to the etchant (comparing to the upper dielectric layer 136 or the sidewall spacer layer 126) when exposing the top electrode 118, thereby providing extra support and protection to the top electrode 118 from being damaged.

FIG. 2 illustrates a cross-sectional view of an integrated circuit device 200 including a memory cell 201 according to some additional embodiments. The memory cell 201 may have the same structure as the memory cell 114 a, 114 b shown in FIG. 1A or FIG. 1B and described above. As shown in FIG. 2, the memory cell 201 can be disposed over a substrate 202. The substrate 202 may be, for example, a bulk substrate (e.g., a bulk silicon substrate) or a silicon-on-insulator (SOI) substrate. One or more shallow trench isolation (STI) regions 204 or oxide-filled trenches are disposed in the substrate 202. A pair of word line transistors 206, 208 is spaced between the STI regions 204. The word line transistors 206, 208 extend parallel to each other, and include word line gates 210 separated from the substrate 202 by word line dielectric layers 212, and source/drain regions 214, 216. The source/drain regions 214, 216 are embedded within the surface of the substrate 202 between the word line gates 210 and the STI regions 204. The word line gates 210 may be, for example, doped polysilicon or a metal, such as titanium nitride or tantalum nitride. The word line dielectric layers 212 may be, for example, an oxide, such as silicon dioxide. A bottom-most ILD layer 238 is disposed overlying the word line transistors 206, 208. The bottom-most ILD layer 238 may be an oxide.

A back-end-of-line (BEOL) metallization stack 218 is arranged over the word line transistors 206, 208. The BEOL metallization stack 218 includes a plurality of metallization layers 222, 224, 226 respectively arranged within the interlayer dielectric layers 220, 228, 230. The metallization layers 222, 224, 226 may be, for example, a metal, such as copper or aluminum. The interlayer dielectric layers 220, 228, 230 may be, for example, a low-κ dielectric, such as porous undoped silicate glass, or an oxide, such as silicon dioxide. Dielectric layers 108, 242 may be disposed to separate the interlayer dielectric layers 220, 228, 230. The metallization layers 222, 224, 226 include a source line 232 coupled to the source/drain region 214 shared by the word line transistors 206, 208. Further, the metallization layers 222, 224, 226 include a bit line connected to the memory cell 201 and further connected to the source/drain region 216 of the word line transistor 206 or the word line transistor 208 through a plurality of metallization lines, such as metallization lines 106, 234, and a plurality of vias, such as vias 132, 110, 240. A contact 236 extends from the metallization line 234 through the bottom-most ILD layer 238 to reach the source/drain region 216. The vias 132, 110, 240 and the contact 236 may be, for example, a metal, such as copper, gold, or tungsten.

The memory cell 201 is inserted between a top metallization line 134 and a bottom metallization line 106. Similar as described above associated with FIG. 1A or FIG. 1B, the memory cell 201 comprises a bottom electrode 112 connecting or seamless contacting a bottom electrode via 110. A switching dielectric 116 is disposed over the bottom electrode 112. A top electrode 118 is disposed over the switching dielectric 116. A sidewall spacer layer 126 extends upwardly along sidewalls of the bottom electrode 112, the switching dielectric 116, and the top electrode 118. A lower etch stop layer 120 is disposed on the sidewall spacer layer 126. An upper dielectric layer 136 is disposed on the lower etch stop layer and overlying the memory cell 201. The upper dielectric layer 136 may be an oxide. The lower etch stop layer 120 has an etch selectivity different from the upper dielectric layer 136 and/or the sidewall spacer layer 126, such that the lower etch stop layer 120 covers and protects the top electrode 118 when the precursor materials of the upper dielectric layer 136 and/or the sidewall spacer layer 126 is etched back to expose the top electrode 118. A top electrode via 132 connects the top electrode 118 to the top metallization line 134. Though the memory cell 201 is shown as inserted between the upper metallization layer 226 and the lower metallization layer 224 in FIG. 2, it is appreciated that the memory cell 201 can be inserted between any two of the metallization layers of the BEOL metallization stack 218.

FIGS. 3-7 illustrate a series of cross-sectional views of some embodiments of a memory device at various stages of manufacture.

As shown in cross-sectional view 300 of FIG. 3, a first memory cell stack 302 a and a second memory cell stack 302 b are formed one next to another over a substrate 102 by depositing a multi-layer stack by a series of vapor deposition techniques (e.g., physical vapor deposition, chemical vapor deposition, etc.) followed by one or more patterning processes. The first memory cell stack 302 a and the second memory cell stack 302 b may be formed with different sizes. Each of the first and second memory cell stacks 302 a, 302 b comprises a bottom electrode 112, a switching dielectric 116 over the bottom electrode 112, a top electrode 118 over the switching dielectric 116, and a sidewall spacer layer 126 alongside sidewalls of the bottom electrode 112, the switching dielectric 116, and the top electrode 118. The sidewall spacer layer 126 may be formed by depositing a dielectric spacer layer on an upper surface of the lower dielectric layer 108, extending along sidewall surfaces of the bottom electrode 112, the switching dielectric 116, and the top electrode 118, and covering a top surface of the top electrode 118. Then an anisotropic etch (e.g. a vertical etch) may be performed to the dielectric spacer layer to remove lateral stretches of the dielectric spacer layer, thereby resulting in the sidewall spacer layer 126. As a result, the sidewall spacer layer 126 may have a top surface lower than that of the top electrode 118. The top surface of the sidewall spacer layer 126 may also be aligned or lower than a top surface of the top electrode 118. The dielectric spacer layer may comprise silicon nitride, tetraethyl orthosilicate (TEOS), silicon-rich oxide (SRO), or a similar composite dielectric film. In some embodiments, the dielectric spacer layer may be formed by a vapor deposition technique (e.g., physical vapor deposition, chemical vapor deposition, etc.).

As shown in cross-sectional view 400 of FIG. 4, a plurality of dielectric layers is formed over and between the first memory cell stack 302 a and the second memory cell stack 302 b. The plurality of dielectric layers may include a lower etch stop layer 120 formed over the substrate 102 between and lining the first and second memory cell stacks 302 a, 302 b, an upper dielectric layer 136 formed over the lower etch stop layer 120, an upper etch stop layer 402 formed over the upper dielectric layer 136, and a polishing precursor layer 404 formed over the upper etch stop layer 402. The lower etch stop layer 120 may be made of a dielectric material different from the sidewall spacer layer 126 and the upper dielectric layer 136. The lower etch stop layer 120 may be, for example, silicon oxynitride (SiON). The upper dielectric layer 136 may be, for example, a low-k or an extreme low-k dielectric. In some embodiments, the upper etch stop layer 402 and the lower etch stop layer 120 are made of the same material. The upper dielectric layer 136 and the polishing precursor layer 404 may be silicon dioxide and may be formed by plasma enhanced atomic layer deposition (PEALD).

As shown in cross-sectional view 500 of FIG. 5, a first planarization/recessing process is performed to partially remove the upper etch stop layer 402 and the polishing precursor layer 404. In some embodiments, the first planarization/recessing process is a chemical-mechanical polishing (CMP) process. The first planarization/recessing process may be substantially non-selective to the upper etch stop layer 402 and the polishing precursor layer 404 such that the upper etch stop layer 402 and the polishing precursor layer 404 can have coplanar top surfaces as the etching result. After the first etching, a portion of the polishing precursor layer 404 and a portion of the upper etch stop layer 402 directly above the first memory cell stack 302 a and the second memory cell stack 302 b are removed by the first planarization/recessing process. A remaining portion of the polishing precursor layer 404 between the first memory cell stack 302 a and the second memory cell stack 302 b has sidewall and bottom surfaces surrounded by the remaining portion of the upper etch stop layer 402. A portion of the upper dielectric layer 136 directly above the memory cell stacks 302 a, 302 b is exposed. The exposed portion of the upper dielectric layer 136 may have a top surface substantially coplanar with the upper etch stop layer 402 or the polishing precursor layer 404.

As shown in cross-sectional view 600 of FIG. 6, a second planarization/recessing process is performed to further lower the plurality of dielectric layers. The polishing precursor layer 404 may be removed and the upper etch stop layer 402 may be exposed at a peripheral region of the memory cell stacks 302 a, 302 b. A portion of the lower etch stop layer 120 directly above the memory cell stacks 302 a, 302 b is exposed. In some embodiments, the second planarization/recessing process is a chemical-mechanical polishing (CMP) process. The second planarization/recessing process may be highly selective to the upper dielectric layer 136 comparing to the upper etch stop layer 402 and the lower etch stop layer 120. For example, the upper dielectric layer 136 (e.g. a PEALD oxide layer) may have a removal rate about 10 times greater than the lower etch stop layer 120 (e.g. a SiON layer) and the upper etch stop layer 402 (e.g. a SiON layer) during the second planarization/recessing process. The lower etch stop layer 120 is more resistive to the etchant (comparing to the upper dielectric layer 136), thereby providing extra support and protection to the top electrode 118 from being damaged. The lower etch stop layer 120 may be made of a material having an etching rate smaller (e.g. about 50% smaller) than that of the sidewall spacer layer 126 (e.g. a SiN layer), such that more support can be provided to the memory cell stacks 302 a, 302 b and peripheral region by the lower etch stop layer 120 and the upper etch stop layer 402 during the first and second planarization/recessing processes.

As shown in cross-sectional view 700 of FIG. 7, a blanket etch is performed to remove the upper etch stop layer 402 (shown in FIG. 6) and to further lower the lower etch stop layer 120 and the upper dielectric layer 136. As an etching result, the top electrodes 118 of the first and second memory cell stacks 302 a, 302 b are exposed. In some embodiments, referring to FIG. 2 for example, after performing the blanket etch, an interlayer dielectric layer 230 is formed overlying the top electrode 118, the sidewall spacer layer 126, and the upper dielectric layer 136. A top electrode via 132 is formed extending through the interlayer dielectric layer 230 to reach on the top electrode 118.

FIG. 8 shows some embodiments of a flow diagram of a method 800 of forming a memory device. Although method 800 is described in relation to FIGS. 3-7, it will be appreciated that the method 800 is not limited to such structures disclosed in FIGS. 3-7, but instead may stand alone independent of the structures disclosed in FIGS. 3-7. Similarly, it will be appreciated that the structures disclosed in FIGS. 3-7 are not limited to the method 800, but instead may stand alone as structures independent of the method 800. Also, while disclosed methods (e.g., method 800) are illustrated and described below as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

At 802, a first memory cell stack and a second memory cell stack are formed one next to another over a substrate by depositing a multi-layer stack followed by one or more patterning processes. A sidewall spacer layer is formed alongside sidewalls of a bottom electrode, switching dielectric, and a top electrode of the memory cell stack. The sidewall spacer layer may be formed to have a top surface lower than that of the top electrode. The top surface of the sidewall spacer layer may also be aligned or lower than a top surface of the top electrode. FIG. 3 illustrates some embodiments of a cross-sectional view 300 corresponding to act 802.

At 804, a plurality of dielectric layers is formed over and between the first memory cell stack and the second memory cell stack. The plurality of dielectric layers may include a lower etch stop layer formed over the substrate between and lining the first and second memory cell stacks, an upper dielectric layer formed over the lower etch stop layer, an upper etch stop layer formed over the upper dielectric layer, and a polishing precursor layer formed over the upper etch stop layer. The lower etch stop layer may be, for example, silicon oxynitride (SiON). FIG. 4 illustrates some embodiments of a cross-sectional view 400 corresponding to act 804.

At 806, a first planarization/recessing process is performed to partially remove the upper etch stop layer and the polishing precursor layer. In some embodiments, the first planarization/recessing process is a chemical-mechanical polishing (CMP) process. The first planarization/recessing process may be substantially non-selective to the upper etch stop layer and the polishing precursor layer. A portion of the polishing precursor layer and a portion of the upper etch stop layer directly above the first and second memory cell stacks are removed by the first planarization/recessing process. A remaining portion of the polishing precursor layer between the first memory cell stack and the second memory cell stack has sidewall and bottom surfaces surrounded by the remaining portion of the upper etch stop layer. A portion of the upper dielectric layer directly above the memory cell stacks is exposed. FIG. 5 illustrates some embodiments of a cross-sectional view 500 corresponding to act 806.

At 808, a second planarization/recessing process is performed to further lower the plurality of dielectric layers. The polishing precursor layer may be removed and the upper etch stop layer may be exposed at a peripheral region of the memory cell stacks. A portion of the lower etch stop layer directly above the memory cell stacks is exposed. In some embodiments, the second planarization/recessing process is a chemical-mechanical polishing (CMP) process. FIG. 6 illustrates some embodiments of a cross-sectional view 600 corresponding to act 808.

At 810, a blanket etch is performed to remove the upper etch stop layer and to further lower the lower etch stop layer and the upper dielectric layer. The top electrodes of the first and second memory cell stacks are exposed. FIG. 7 illustrates some embodiments of a cross-sectional view 700 corresponding to act 810.

FIGS. 9-13 illustrate a series of cross-sectional views of some embodiments of a memory device at various stages of manufacture.

As shown in cross-sectional view 900 of FIG. 9, a first memory cell stack 302 a and a second memory cell stack 302 b are formed one next to another over a substrate 102 by depositing a multi-layer stack by a series of vapor deposition techniques (e.g., physical vapor deposition, chemical vapor deposition, etc.) followed by one or more patterning processes. The first memory cell stack 302 a and the second memory cell stack 302 b may be formed with different sizes. Each of the first and second memory cell stacks 302 a, 302 b comprises a bottom electrode 112, a switching dielectric 116 over the bottom electrode 112, and a top electrode 118 over the switching dielectric 116. In some embodiments, the bottom electrode 112 is coupled to a bottom electrode via 110 surrounded by a lower dielectric layer 108. A sidewall spacer layer 126 is formed by depositing a dielectric spacer layer in conformal and directly on the lower dielectric layer 108 and extends upwardly along sidewalls of the bottom electrode 112, the switching dielectric 116, and the top electrode 118. The dielectric spacer layer may comprise silicon nitride, tetraethyl orthosilicate (TEOS), silicon-rich oxide (SRO), or a similar composite dielectric film. In some embodiments, the dielectric spacer layer may be formed by a vapor deposition technique (e.g., physical vapor deposition, chemical vapor deposition, etc.).

As shown in cross-sectional view 1000 of FIG. 10, a plurality of dielectric layers is formed over and between the first memory cell stack 302 a and the second memory cell stack 302 b and follows the curvature of the memory cell stacks 302 a, 302 b. The plurality of dielectric layers may include a lower etch stop layer 120 formed directly on the sidewall spacer layer 126, an upper dielectric layer 136 formed on the lower etch stop layer 120, an upper etch stop layer 1002 formed over the upper dielectric layer 136, an oxygen-containing dielectric layer 1004 formed over the upper etch stop layer 1002, and a polishing precursor layer 1006 formed over the oxygen-containing dielectric layer 1004. The lower etch stop layer 120 may be made of a dielectric material different from the sidewall spacer layer 126 and the upper dielectric layer 136. The lower etch stop layer 120 may be, for example, silicon oxynitride (SiON). The upper dielectric layer 136 may be, for example, a low-k or an extreme low-k dielectric. In some embodiments, the upper etch stop layer 1002 and the lower etch stop layer 120 are made of the same material. The upper dielectric layer 136 may be silicon dioxide and may be formed by plasma enhanced atomic layer deposition (PEALD). The oxygen-containing dielectric layer 1004 may comprise tetraethyl orthosilicate (TEOS). The polishing precursor layer 1006 may comprise anti-reflective coating material (e.g. carbon-containing BARC material).

As shown in cross-sectional view 1100 of FIG. 11, a first planarization/recessing process is performed to partially remove the upper etch stop layer 1002, the oxygen-containing dielectric layer 1004, and the polishing precursor layer 1006. In some embodiments, the first planarization/recessing process comprises a dry etching back process that is selective to the polishing precursor layer 1006 comparing to the upper etch stop layer 1002. For example, the dry etching back process has an etching rate ratio of the polishing precursor layer 1006 to the upper etch stop layer 1002 greater than 6:1. The dry etching back is stopped on the upper etch stop layer 1002 by detecting oxygen of the oxygen-containing dielectric layer 1004. Then an over etch is performed to remove the oxygen-containing dielectric layer 1004 and the upper etch stop layer 1002 and to expose the upper dielectric layer 136 above the first memory cell stack 302 a and the second memory cell stack 302 b.

As shown in cross-sectional view 1200 of FIG. 12, a second planarization/recessing process is performed to further lower the plurality of dielectric layers. The polishing precursor layer 1006 may be removed and the upper etch stop layer 1002 may be exposed at a peripheral region of the memory cell stacks 302 a, 302 b. A portion of the lower etch stop layer 120 directly above the memory cell stacks 302 a, 302 b is exposed. In some embodiments, the second planarization/recessing process is a chemical-mechanical polishing (CMP) process. The second planarization/recessing process may be highly selective to the upper dielectric layer 136 comparing to the upper etch stop layer 1002 and the lower etch stop layer 120. For example, the upper dielectric layer 136 (e.g. a PEALD oxide layer) may have a removal rate about 10 times greater than the lower etch stop layer 120 (e.g. a SiON layer) and the upper etch stop layer 402 (e.g. a SiON layer) during the second planarization/recessing process. The lower etch stop layer 120 is more resistive to the etchant (comparing to the upper dielectric layer 136), thereby providing extra support and protection to the top electrode 118 from being damaged. The lower etch stop layer 120 may be made of a material having an etching rate smaller (e.g. about 50% smaller) than that of the sidewall spacer layer 126 (e.g. a SiN layer), such that more support can be provided to the memory cell stacks 302 a, 302 b and peripheral region by the lower etch stop layer 120 and the upper etch stop layer 1002 during the first and second planarization/recessing processes.

As shown in cross-sectional view 1300 of FIG. 13, a blanket etch is performed to remove the upper etch stop layer 1002 (shown in FIG. 12 and to further lower the lower etch stop layer 120 and the upper dielectric layer 136. As an etching result, the top electrodes 118 of the first and second memory cell stacks 302 a, 302 b are exposed. In some embodiments, referring to FIG. 2 for example, after performing the blanket etch, an interlayer dielectric layer 230 is formed overlying the top electrode 118, the sidewall spacer layer 126, and the upper dielectric layer 136. A top electrode via 132 is formed extending through the interlayer dielectric layer 230 to reach on the top electrode 118.

FIG. 14 shows some embodiments of a flow diagram of a method 1400 of forming a memory device. Although method 1400 is described in relation to FIGS. 9-13, it will be appreciated that the method 1400 is not limited to such structures disclosed in FIGS. 9-13, but instead may stand alone independent of the structures disclosed in FIGS. 9-13. Similarly, it will be appreciated that the structures disclosed in FIGS. 9-13 are not limited to the method 1400, but instead may stand alone as structures independent of the method 1400. Also, while disclosed methods (e.g., method 1400) are illustrated and described below as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

At 1402, a first memory cell stack and a second memory cell stack are formed one next to another over a substrate by depositing a multi-layer stack followed by one or more patterning processes. A sidewall spacer layer is formed on a lower dielectric layer alongside sidewalls of the memory cell stack. The sidewall spacer layer may be formed in conformal. FIG. 9 illustrates some embodiments of a cross-sectional view 900 corresponding to act 1402.

At 1404, a plurality of dielectric layers is formed over and between the first memory cell stack and the second memory cell stack. The plurality of dielectric layers may include a lower etch stop layer formed over the substrate between and lining the first and second memory cell stacks, an upper dielectric layer formed over the lower etch stop layer, an upper etch stop layer formed over the upper dielectric layer, and an oxygen-containing dielectric layer and a polishing precursor layer formed over the upper etch stop layer. The lower etch stop layer may be, for example, silicon oxynitride (SiON). FIG. 10 illustrates some embodiments of a cross-sectional view 1000 corresponding to act 1404.

At 1406, a first planarization/recessing process is performed to partially remove the upper etch stop layer and the polishing precursor layer. In some embodiments, the first planarization/recessing process comprises a dry etching back process that is selective to the polishing precursor layer. The dry etching back process stops on the oxygen-containing dielectric layer and is followed by a more precise controlled etch to reach a planar surface after the etching. After the first planarization/recessing process, a portion of the upper dielectric layer directly above the memory cell stacks is exposed. FIG. 11 illustrates some embodiments of a cross-sectional view 1100 corresponding to act 1406.

At 1408, a second planarization/recessing process is performed to further lower the plurality of dielectric layers. The polishing precursor layer may be removed and the upper etch stop layer may be exposed at a peripheral region of the memory cell stacks. A portion of the lower etch stop layer directly above the memory cell stacks is exposed. In some embodiments, the second planarization/recessing process is a chemical-mechanical polishing (CMP) process. FIG. 12 illustrates some embodiments of a cross-sectional view 1200 corresponding to act 1408.

At 1410, a blanket etch is performed to remove the upper etch stop layer and to further lower the lower etch stop layer and the upper dielectric layer. The top electrodes of the first and second memory cell stacks are exposed. FIG. 13 illustrates some embodiments of a cross-sectional view 1300 corresponding to act 1410.

It will be appreciated that while reference is made throughout this document to exemplary structures in discussing aspects of methodologies described herein that those methodologies are not to be limited by the corresponding structures presented. Rather, the methodologies (and structures) are to be considered independent of one another and able to stand alone and be practiced without regard to any of the particular aspects depicted in the Figs. Additionally, layers described herein, can be formed in any suitable manner, such as with spin on, sputtering, growth and/or deposition techniques, etc.

Also, equivalent alterations and/or modifications may occur to those skilled in the art based upon a reading and/or understanding of the specification and annexed drawings. The disclosure herein includes such modifications and alterations and is generally not intended to be limited thereby. For example, although the figures provided herein are illustrated and described to have a particular doping type, it will be appreciated that alternative doping types may be utilized as will be appreciated by one of ordinary skill in the art.

Thus, as can be appreciated from above, the present disclosure provides a method for forming a memory device. The method comprises forming a memory cell over a substrate and forming a sidewall spacer layer along the memory cell. The method further comprises forming a lower etch stop layer on the sidewall spacer layer and forming an upper dielectric layer on the lower etch stop layer. The method further comprises performing a first etching process to etch back the upper dielectric layer using the lower etch stop layer as an etch endpoint.

In another embodiment, the present disclosure relates to a method for forming a memory device. The method comprises forming a magnetoresistive random access memory (MRAM) cell over a substrate and forming a sidewall spacer layer along the MRAM cell. The method further comprises forming a lower etch stop layer on the sidewall spacer layer and forming an upper dielectric layer on the lower etch stop layer. The method further comprises performing a first etching process to etch back the upper dielectric layer using the lower etch stop layer as an etch endpoint to stop the upper dielectric layer etch back.

In yet another embodiment, the present disclosure relates to a memory device. The memory device comprises a memory cell disposed over a lower dielectric layer over a substrate and a sidewall spacer layer disposed along the memory cell. The memory device further comprises a lower etch stop layer disposed on the sidewall spacer layer and an upper dielectric layer disposed on the lower etch stop layer. The sidewall spacer layer extends along an upper surface of the lower dielectric layer and separates the lower etch stop layer from the lower dielectric layer.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method of forming a memory device, comprising: forming a memory cell over a substrate; forming a sidewall spacer layer along the memory cell; forming a lower etch stop layer on the sidewall spacer layer; forming an upper dielectric layer on the lower etch stop layer; and performing a first etching process to etch back the upper dielectric layer using the lower etch stop layer as an etch endpoint.
 2. The method of claim 1, prior to performing the first etching process, further comprising: forming an upper etch stop layer over the upper dielectric layer; and performing a first chemical-mechanical polishing (CMP) process to expose the upper dielectric layer directly above the memory cell.
 3. The method of claim 1, after performing the first etching process, further comprising: performing a blanket etch to remove the upper etch stop layer and to further lower the upper dielectric layer and expose the memory cell.
 4. The method of claim 1, further comprising: forming a top interlayer dielectric layer over the upper dielectric layer; and forming a top metallization line and a top electrode via through the top interlayer dielectric layer to reach on the memory cell.
 5. The method of claim 1, forming the memory cell comprises: forming a bottom electrode over the substrate; forming a switching dielectric over the bottom electrode; and forming a top electrode over the switching dielectric.
 6. The method of claim 1, wherein the memory cell is a magnetoresistive random access memory (MRAM) cell.
 7. The method of claim 1, wherein the memory cell is formed between fabrication processes of a lower metallization line and an upper metallization line.
 8. The method of claim 1, wherein the lower etch stop layer is made of silicon oxynitride.
 9. The method of claim 1, wherein forming the lower etch stop layer comprises forming a dielectric material along a sidewall of the sidewall spacer layer.
 10. The method of claim 1, wherein forming the lower etch stop layer comprises depositing the lower etch stop layer on the sidewall spacer layer.
 11. The method of claim 1, wherein the lower etch stop layer is formed with a dielectric material having an etch selectivity different from the upper dielectric layer with respect to the etchant of the first etching process, such that the lower etch stop layer is retained to protect the memory cell from damage.
 12. The method of claim 1, wherein the lower etch stop layer has a top surface coplanar with a top surface of the upper dielectric layer.
 13. A method of forming a memory device, comprising: forming a magnetoresistive random access memory (MRAM) cell over a substrate; forming a sidewall spacer layer along the MRAM cell; forming a lower etch stop layer on the sidewall spacer layer; forming an upper dielectric layer on the lower etch stop layer; and performing a first etching process to etch back the upper dielectric layer using the lower etch stop layer as an etch endpoint to stop the upper dielectric layer etch back.
 14. The method of claim 13, prior to performing the first etching process, further comprising: forming an upper etch stop layer over the upper dielectric layer; and forming a polishing precursor layer over the upper etch stop layer; wherein a portion of the polishing precursor layer directly above the MRAM cell is removed by the first etching process and a remaining portion of the polishing precursor layer on sides of the MRAM cell has sidewall and bottom surfaces surrounded by the upper etch stop layer.
 15. The method of claim 14, further comprising: performing a dry etching back process to the polishing precursor layer prior to performing the first etching process; wherein the dry etching back process has an etching rate ratio of the polishing precursor layer to the upper dielectric layer greater than 6:1.
 16. The method of claim 13, after performing the first etching process, further comprising: performing a blanket etch to remove the upper etch stop layer and to further lower the upper dielectric layer and expose the memory cell.
 17. A memory device, comprising: a memory cell disposed over a lower dielectric layer over a substrate; a sidewall spacer layer disposed along the memory cell; a lower etch stop layer disposed on the sidewall spacer layer; and an upper dielectric layer disposed on the lower etch stop layer; wherein the sidewall spacer layer extends along an upper surface of the lower dielectric layer and separates the lower etch stop layer from the lower dielectric layer.
 18. The memory device of claim 17, wherein the lower etch stop layer is made of silicon oxynitride and the sidewall spacer layer is made of silicon nitride.
 19. The memory device of claim 17, wherein the lower etch stop layer, the upper dielectric layer, and the sidewall spacer layer have top surfaces aligned with one another.
 20. The memory device of claim 17, further comprising: a bottom metallization line surrounded by a bottom interlayer dielectric layer and electrically coupled to a bottom electrode of the memory cell; and a top metallization line surrounded by a top interlayer dielectric layer and electrically coupled to a top electrode of the memory cell. 